Roller assembly and method of making the same

ABSTRACT

A roller assembly having an inner stator member and an outer roller member rotatably supported on the stator member and method of making the same in which the roller member is molded in an annular form with an inner bearing surface of circular crosssection extending axially through the roller member, and the inner stator member is thereafter injection molded inside the inner bearing surface, of a plastic material having a molding shrinkage characteristic such as to provide sufficient clearance between the stator and roller members for a running fit therebetween. In molding the stator member in the roller member, circumferentially spaced portions of the inner bearing surface of the roller member are preferably sealed from the mold cavity for the stator member so that the stator member is formed with a noncircular cross-section with only circumferentially spaced portions having a shape conforming to and in a running fit with the inner bearing surface on the roller member.

United States Patent [1 1 Peura [451 Jan. 15, 1974 ROLLER ASSEMBLY ANDMETHOD OF MAKING THE SAME [75] Inventor:

[73] Assignee: Consolidated Foods Corporation,

Chicago, Ill.

22 Filed: July 17,1972

21 Appl. No.: 272,553

Warren A. Peura, Madison, Wis.

[52] U.S. Cl. 74/2303, 264/242 [56] References Cited UNITED STATESPATENTS 6/ l 971 Fischer 74/230.4 7/1971 Memory... 12/1971 Funahashi264/242 Primary Examiner-Leonard H. Gerin AttorneyVernon J. Pillote 5 7ABSTRACT A roller assembly having an inner stator member and an outerroller member rotatably supported on the stator member and method ofmaking the same in which the roller member is molded in an annular formwith an inner bearing surface of circular cross-section extendingaxially through the roller member, and the inner stator member isthereafter injection molded inside the inner bearing surface, of aplastic material having a molding shrinkage characteristic. such as toprovide sufficient clearance between the stator and roller members for arunning flit therebetween. ln molding the stator member in the rollermember, circumferentially spaced portions of the inner bearing surfaceof the roller member are preferably sealed from the mold cavity for thestator member so that the stator member is formed with a non-circularcrosssection with only circumferentially spaced portions having a shapeconforming to and in a running fit with the inner bearing surface on theroller member.

16 Claims, 11 Drawing Figures PAIENTED I 51914 i 3. 785.2 1 T sum 2 or 2Zia ROLLER ASSEMBLY AND METHOD OF MAKING THE SAME BACKGROUND OF THEINVENTION Various different arrangements have heretofore been proposedfor making roller assemblies for use as wheels, bearings, pulleys andthe like. It is common practice to separately mold the roller member andthe axle and to thereafter assemble the roller and axle and secure astop means on the axle to prevent the roller from moving axially off theaxle. However, the separate molding and handling of the severalparts andthe subsequent assembly step increases the overall cost of such rollerassemblies. It has also been proposed, as disclosed in the US. Pat. toSmith, No. 2,724,867 to mold the rim and axle simultaneously of the samematerial, with a flange on one end of the axle connected by a thinfrangible web to one end of the roller in alignment with the axleopeningtherein, so that the roller could thereafter be assembled on theaxle by rupturing the frangible web and shifting the roller axially overthe flange onto the axle. This roller construction and procedure,however, necessitates forming the roller and axle from the same materialand also limits the size of the flange for retaining the roller on theaxle to one having an interference fit with the axle opening in theroller. It has also been proposed, as disclosed in the U. S. Pat. to

Ferdig, No. 3,206,992 to simultaneously mold the outer roller and axleof the same material with the axle inside the outer roller but separatedtherefrom by a thin mold sleeve to provide a running clearance betweenthe roller and axle. That construction and procedure,

, however, necessitated a relatively complex mold apparatus and,moreover, the flange for retaining the roller onthe axle had to be madesufficiently small and thin so as to be-deflectable during withdrawal ofthe mold sleeve from between the roller and axle.

SUMMARY OF THE INVENTIGN The present invention relates to a rollerassembly having an inner stator member and an outer roller memberrotatably supported on the stator and method of making the same in whichthe roller member is molded in an annular form with an inner bearingsurface of circular cross-section extending axially through the rollermember, and the stator member is thereafter injection molded inside theinner bearing surface of the roller member of a plastic material havingmolding shrinkage characteristics such as to provide sufficientclearance between the roller and stator members for a running fittherebetween. In molding the stator member inside the roller member,circumferentially spaced portions of the inner bearing surface on theroller member are preferably sealed from the mold cavity for the statormember so that the stator member has a noncircular configuration withonly circumferentially spaced portions shaped in conformity with theinner bearing surface on the roller member. The roller and statormembers are advantageously molded of different plastic materials, withthe plastic material for the outer roller member being selected toprovide the desired rigidity and surface characteristics for its use asa wheel, hearing or pulley, and the plastic material for the innerstator member being selected to provide low friction characteristics.The successive moldings of the roller member and the stator member inthe roller member are preferably effected in rapid succession with thestator member being injection molded to the roller member after theroller member has solidified but before it has cooled to ambienttemperature, and the plastic materials for the stator and roller membersare selected such that the stator member has a lower melting point and ahigher molding shrinkage characteristic than the roller member and suchas to provide the desired running fit therebetween when the parts havecooled. Since the stator member is molded inside the annular bearingsurface on the roller member, the annular bearing surface on the rollermember can be formed with a non-linear configuration such that the innerbearing surface and the conforming portions on the stator member preventaxial movement while permitting free rotational movement of the rollermember relative to the stator member.

These and other aspects of the invention will be more fully understoodfrom the following detailed description and the accompanying drawings inwhich:

FIG. 1 is a side view of a preferred embodiment of a roller assembly;

FIG. 2 is a sectional view through the roller assembly taken on a plane2-2 of FIG. 1;

FIG. 3 is a edge elevational view of the roller assembly shown mountedon a support;

FIG. 4 is a sectional view taken on the broken line section 4-4 of FIG.1;

FIG. 5 is a side view of a modified form of roller assembly;

FIG. 6 is a sectional view taken on a plane 6-6 of FIG. 5;

FIG. 7 is a sectional view through a mold assembly illustrating theformation of the outer roller member;

FIG. 8 is a sectional view through'the mold assembly taken on the plane88 of FIG. 7;

FIG. 9 is a sectional view through the mold assembly for molding theinner stator member of the wheel assembly of FIGS. 1-4;

FIG. 10 is a sectional view through the mold assembly taken on the plane10-l0 of FIG. 9; and

FIG. 11 is a sectional view through a modified form of mold assembly forforming the stator member of the roller assembly of FIGS. 5 and 6.

The roller assembly in general includes an outer roller member 10 ofannular configuration, and an inner stator member 11 injection molded inthe roller member and having a mold shrink clearance therewith toprovide a running fit between the roller and stator members. The rollermember is initially formed to have an inner bearing surface of circularcross-section, and the stator member is thereafter injection molded intothe roller member so that the stator member has at leastcircumferentially spacedportions conforming to the shape of the bearingsurface. The stator member is injection molded of a plastic materialhaving molding shrinkage characteristics to provide sufficient clearancebetween the roller and the stator to provide a running fit therebetween.Preferably, the outer roller member and the inner stator member areformed as successive stages of a two-step injection molding process and,in order to minimize the overall cycle time to complete the two-stepmolding process, the plastic materials for the inner and outer membersare selected so that the plasticmaterial used in the inner stator memberhas a relatively higher molding shrinkage characteristic and arelatively lower melting temperature than the material used for theouter roller member.

The outer roller member 10 is formed in annular shape having an outerrim surface 100, opposed end faces 10b, and aninner bearing surface 10sof circular cross-section. In order to inhibit relative axial movementbetween the roller and stator after the roller assembly is completed,the inner bearing surface 10c is formed with a longitudinally varyingdiameter, the diameter being a minimum intermediate the ends of theroller and being relatively larger adjacent opposite end walls 10b.Preferably, the inner bearing surface is longitudinally convex as bestshown in FIGS. 2, 4 and 6, with a radius of curvature that is largerthan the axial length of the roller. The circular rim surface 10a on theroller can be formed with different longitudinal configurations. In theembodiment illustrated, the roller assembly is adapted for use as apulley and is formed with a peripheral groove. As will be readilyapparent, the outer rim surface 10a can be made flat, flanged or convex,if desired for use as a wheel or bearing.

In the preferred embodiment shown in FIGS. l4, the stator member isinjection molded in the outer roller member to have a non-circular andpreferably generally triangular configuration, with circumferentiallyspaced portions llashaped in conformity with the inner bearing surfaceon the roller member, and with intermediate portions llbspaced radiallyinwardly from the inner bearing surface. In the form shown, theintermediate portions 11b of the stator member are generally planar andextend in chordal fashion to the major outer diameter of the innerbearing surface 100 on the roller member. Since the inner bearingsurface 100 is longitudinally convex, the circumferentially spacedportions 11a on the stator member which engage the inner bearing surfaceon the roller member, have a maximum circumferential width adjacent theminor diameter of the inner bearing surface and decrease in widthtowards the ends of the roller so as to have a generally ellipticalshape, as shown in FIG. 4. The shape of the inner stator member can ofcourse be modified to increase the width of the surfaces 110 thatcontact the inner bearing surface 10 c. The roller illustrated in FIGS.1-4 is adapted for mounting on a flat support surface and at least oneof the end faces 11d of the stator member is preferably offset outwardlyfrom the plane of the corresponding end face 10bon the roller, toprovide a working clearance between the roller and the support 18. Afastener receiving opening le is formed in the stator member forreceiving a fastener 19 for mounting the roller assembly on the support18.

The outer roller member 10 in the embodiment of the roller shown inFIGS. and 6 is the same as that illustrated and described in connectionwith FIGS. I-4 and like numerals are used to designate the correspondingparts. In the embodiment of FIGS. 5 and 6,.

however, a modified inner stator member 11 is injection molded in theouter roller member. Stator member 11' is injection molded so that itsouter periphery 11a is of circular cross-section and is shaped inconformity with, and has a shrink clearance relative to, the innerbearing surface c on the outer roller member. As in the precedingembodiment, at least one of the end faces Ildthe inner stator member ispreferably offset outwardly from the corresponding end face of theroller member to provide a running clearance for the roller member whenthe latter is mounted on a flat support surface, and an opening l0e' isprovided in the stator member 11' for receiving a fastener for mountingthe same.

While the outer roller member can be formed in various different waysand of different materials, it is preferably formed by injection moldinga plastic material as a first step in a two-step injection moldingprocess for forming the roller assembly. The mold assembly utilized forforming the outer roller member will vary somewhat, dependent largely onthe configuration of the outer rim surface 10a to be formed. In the moldassembly illustrated in FIGS. 7 and 8, a pair of mold members 21 and 22are supported for relative movement in a direction indicated by thearrow 23 and have side faces 21a, 22a, shaped to form the opposed endfaces 10b on the roller member, and generally frustoconical bosses 21b,22b having peripheral surfaces 21c and 220 respectively of circularcross-section and longitudinally varying diameter to form the innerbearing surface 10c of the roller member. Preferably, the parting line21d of the mold members is located immediately between the ends of theroller member. In order to form the concave periphery on the outer rimsurface 10a of the roller member, a pair of mold members 25, 26 aremounted for relative movement in the direction indicated by the arrow27, and the mold members 25, 26 have opposed semi-circular recesses 25a,26a with a transverse configuration such as to form the concaveperiphery on the roller member. As will be understood, the transverselymovable mold members 25, 26 would not be required if the periphery ofthe roller were flat or convex, for use as wheel or bearing. In suchwheel or bearing assemblies, the outer periphery rim surface 10a can beformed by annular walls on the mold members 21 and 22. Asdiagrammatically illustrated in FIG. 7, the plastic material for formingthe outer roller member is fed from an injection molding apparatus 20through sprue gates 20a to the mold cavity.

The inner stator member 11 is injection molded of a plastic materialinside the outer roller member so as to have portions conforming to theinner bearing surface of the roller member and to have a shrinkclearance therewith. Molding of the inner stator member is effected bysealingly engaging the end faces 10b of the outer roller member betweena pair of mold members 31, 32, (FIGS. 9 and 10) to form a mold cavityinside the outer roller member. The mold members 31 and 32 are alsoformed with a plurality of circularly spaced projections 31a, 32a, eachhaving arcuate outer surfaces 31b, 32b, shaped to conform withcircumferentially spaced portions of the inner bearing surface on theouter roller member, and inner surfaces 310, 32c shaped to form theintermediate portions on the inner stator member. The projections 31a,32a are attached to or formed integral with the respective mold members31 and 32 and located thereon so as to sealingly engagecircumferentially spaced portions of the inner bearing surface on theouter roller member to thereby define a non-circular mold cavity in theinner bearing member in which those portions of the inner bearingsurface, intermediate the circumferentially spaced portions engaged bythe projections 31a and 32a, form walls of the mold cavity. The moldmembers 31 and 32 are also recessed slightly as indicated at 31e, 32s toform the end faces 11d on the inner stator member which are offsetoutwardly from the corresponding end faces on the inner roller member,and axial projections 31f, 32f are provided on the mold members to formthe fastener receiving opening le in the stator member. The plasticmaterial is then injected into the mold and allowed to cool sufficientto at least solidify before removing the mold members and the completedroller assembly from the mold. Because of the high molding pressuresutilized in injection moldings, it is desirable to radially support orconfine the outer roller member during the injection molding operationand, as diagrammatically shown in FIGS. 9 and 10, the mold members 25,26, previously utilized in shaping the outer rim surface of the rollermember, are conveniently utilized for this purpose. As diagrammaticallyshown in FIG. 9, plastic material for the inner stator member is fedfrom an injection molding apparatus 40 through sprue gates 40a to themold cavity.

Molding of the inner stator member in the roller assembly in FIGS. and 6is effected in a manner similar to that previously described, butwithout engaging the mold members against the inner bearing surface.Thus, as shown in FIG. 11, mold members 31', 32' are provided with sidefaces 31a, 32a arranged to engage opposite sides of the outer rollermember, and recessed faces 3le, 32e' arranged to form the end faces onthe inner stator member. Plug members 31]", 32] are provided on the moldmembers 31, 32 to form the fastener receiving passage in the innerstator member. In molding this form of roller assembly, the plasticmaterial is injection molded into the cavity inside the outer rollermember so as to have an annular outer configuration conforming with theinner bearing surface c on the outer roller member, with a shrinkclearance therewith after the plastic cools. As previously discussed,the outer roller member is preferably radially supported during moldingof the inner stator member and this can conveniently be effected by themold members 25, 26. Satisfactory roller operation necessitates a veryfree running fit between the outer roller member and the inner statormember. The materials utilized in molding the outer roller member andinner stator member are selected to provide the necessary shrinkage fora free running fit and, in addition, the materials are selected so as toavoid damage to the inner bearing surface 100 on the outer roller memberduring injection molding of the inner stator member therein.Advantageously, the inner stator member is formed ofa plastic materialhaving high lubricity, that is a relatively low coefficient to friction,and the outer roller member is formed of a different plastic materialwhich is preferably relatively harder. Various different combinations ofplastic materials can be used and fiberglass reinforcement can beadvantageously employed in the plastic for the outer roller to reducemolding shrinkage and provide greater rigidity. For example, goodresults have been achieved with the outer roller member formed frompolytetramethylene terephthalate plastic, sometimes identified aspolyterephthalate of the glass reinforced type such as marketed byEastman Chemical Products, Inc. of Kingsport, Tenn. under the trademarkTenite"- Polyterephthalate 6691. This material has a crystalline meltingpoint of about 437F. and can be injection molded at temperatures between480 and 520, and the polymer crystallizes rapidly at temperaturesbetween 85 and 300F. so that mold temperatures in this range may beused. This glass reinforced material has a relatively low moldingshrinkage characteristic of the order of about 0.003 inches per inch.

The plastic material used for forming the inner stator member isselected to have a lower crystalline melting temperature, to allowmolding at temperatures below the melting temperature of the roller, anda relatively higher molding shrinkage characteristic to providesufficient clearance between the roller and stator when they are cooledto normal ambient temperature (about F.) Preferably the plastic materialused for the stator is also of a type having a low coefficient offriction. For example, the inner stator member can be formed of apolyacetal based oil lubricated plastic such as distributed by CadillacChemical Co. under the mark OILON Pv 80. This is a polyacetal plastichaving a relatively lower molding temperature and a relatively highermolding shrinkage characteristic than the polyterephthalate used for theouter roller. Thus, the

Oilon Pv has a molding shrinkage characteristic of the range of 0.024 to0.032 inches per inch and provides adequate shrink clearance for a goodrunning fit with the glass reinforced polyterephthalate roller describedabove, on even relatively small size roller assemblies in which theinner bearing surface has a diameter of only about three-eighths toseven-sixteenths inch. In addition, the plastic is highly lubricatedwith a petroleum based lubricant and has a relatively low coefficient tofriction, for example, 0.05 to 0.l0 against polished metal. Otherplastic materials can be used for the roller and stator members providedthey have the proper relative mold shrinkage characteristics to provideadequate clearance for a free running fit when the parts are cooled tonormal ambient temperatures. For example, high density polyethylene maybe used for the roller, with the polyethyene preferably glass reinforcedto reduce shrinkage, and polypropylene used for the stator.Alternatively, nylon can be used for the roller and polypropylene or apolyacetal plastic for the stator. The molding shrinkage characteristicsof plastic are average characteristics and the amount of shrinkage thatwill occur in different portions of the part being molded will vary withvarious factors including shape and thickness of the part, location ofthe sprue gates in the molds, etc. While satisfactory roller assemblieswere made of the forms shown in FIGS. 5 and 6, some difficulties wereencountered in obtaining uniformly consistent free runningcharacteristics :in the roller assemblies. Markedly improved consistencyof results were achieved with the roller assembly shown in FIGS. 1-4molded in the manner shown in FIGS. 7-l0. It is considered that theconfining of the injection molding of the inner stator member tocircumferentially spaced locations on the outer roller member improvesthe overall roller assembly since it reduces the area of the innerroller member exposed to the relatively high molding pressures l2 -01,600 p.s.i.), and hence reduces distortion of the outer roller memberduring injection molding of the inner stator member. In addition, it isconsidered that the mold projections which formed a non-circularconfiguration of the inner stator member achieved better control of theshrinkage of the inner stator member. Moreover, the final rollerassembly with the non-circular inner stator member has a reduced contactarea between the inner and outer members, which is considered to aid inreducing the overall friction therebetween, the generally triangular orthree legged configuration being preferred because of its self centeringaction which can better accommodate any out of round characteristic inthe outer roller member.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:

1. A method of making a roller assembly including an inner stator memberand an outer roller member rotatably and axially non-slidably supportedon the stator member comprising: molding an outer roller member of afirst plastic material in an annular shape having a circular outer rimsurface; end faces, and a circular inner bearing surface having aminimum internal diameter intermediate said end faces and a relativelylarger diameter adjacent said end faces, sealingly engaging end faces ofthe outer roller member between mold members shaped to form an enclosedmold cavity inside the annular roller member with at leastcircumferentially spaced portions of the inner bearing surface beingwall portions of the mold cavity, injecting a heat melted charge of asecond plastic into said mold cavity to fill the same, and cooling thecharge of the second plastic to a solid state before removing the moldmembers to provide a rigid stator member having at least portions of itsouter periphery shaped in conformity with the inner bearing surface onthe roller member, said second plastic material having molding shrinkagecharacteristics to provide sufficient clearance for a running fitbetween said portions of the stator member and said inner bearingsurface on the outer roller member.

2. A method of making a roller assembly according to claim 1 whereinsaid second plastic material has higher molding shrinkagecharacteristics than said first plastic material.

3. A method of making a roller assembly according to claim 1 whereinsaid first plastic material is reinforced with glass fibers and has alower molding shrinkage characteristic than said second plasticmaterial.

4. A method of making a roller assembly according to claim 1 whereinsaid second plastic material has a melt temperature substantially belowthe melt temperature of said first plastic material and said secondplastic material has mold shrinkage characteristics higher than saidfirst plastic material.

5. A method of making a roller assembly including an inner stator memberand an outer roller member rotatably supported on the stator membercomprising, molding a rigid outer roller member of a first plasticmaterial in an annular shape having a circular inner bearing surface,sealingly engaging mold members with the end faces of the outer rollermember and with only circumferentially spaced portions of the innerbearing surface to form a non-circular mold cavity in the annular rollermember in which other portions of the inner bearing surface intermediatesaid circumferentially spaced portions provide wall portions of the moldcavity, injecting a heat melted charge of a second plastic material intothe mold cavity to fill the same, cooling the charge of the secondplastic material sufficient to solidify the charge before removing themold members to provide a rigid non-circular stator member havingcircumferentially spaced portions shaped in conformity with said innerbearing surface, said second plastic material having mold shrinkcharacteristics to provide a sufficient clearance for a running fitbetween said circumferentially spaced portions on the stator member andsaid inner bearing surface on the outer roller member.

6. A method of making a roller assembly according to claim 5 whereinnon-circular mold cavity has a triangular configuration.

7. A method of making a roller assembly according to claim 5 in whichsaid second plastic material has molding shrinkage characteristicshigher than said first plastic material.

8. A method of making a roller assembly according to claim 5 whereinsaid second plastic material has a higher molding shrinkagecharacteristic and a lower melting temperature than said first plasticmaterial.

9. A method of making a roller assembly according to claim 8 whereinsaid second plastic material has a lower coefficient of friction thansaid first plastic material.

10. A method of making a roller assembly according to claim 5 whereinsaid circular inner bearing surface is formed with an axially varyingdiameter.

11. A method of making a roller assembly according to claim 5 whereinsaid inner bearing surface of said outer roller member is formed with alongitudinally varying diameter relatively larger adjacent said endwalls than at a location intermediate said end walls and saidcircumferentially spaced portions on the hub member conform to saidlongitudinally varying diameter.

12. A roller assembly comprising: a rigid outer roller member formed ofa first plastic material having a circular outer rim surface; end faces,and a circular inner bearing surface of longitudinally varying diameterextending between said end faces coaxial with said outer rim surface, aninner stator member injection molded of a second plastic material insaid inner bearing surface to have at least circumferentially spacedportions of its outer periphery shaped to conform with thelongitudinally varying diameter of the inner bearing surface on theouter roller member, and said second plastic material having a moldingshrinkage characteristic sufficiently high to provide clearance for afree running fit with said roller member when said stator member iscool.

13. A roller assembly according to claim 12 wherein the diameter of saidinner bearing surface is a maximum adjacent said end faces and a minimumat a location spaced inwardly from said end faces of the outer rollermember.

14. A roller assembly comprising: a rigid outer roller member formed ofa first plastic material having a circular outer rim surface; end faces,and a circular inner bearing surface of axially varying diameterextending between said end faces coaxial with said outer rim surface,and an inner stator member injection molded of a second plastic materialin said inner bearing surface to have circumferentially spaced portionsof its outer periphery shaped to conform with the longitudinally varyingdiameter of the inner bearing surface on the outer rimmember and have aclose running fit therewith, the peripheral portions of said statormember intermediate said circumferentially spaced portions being spacedradially inwardly from said circumferentially spaced portions and out ofrunning engagement with said inner bearing surface.

15. A roller assembly according to claim 14 wherein said inner statormember has a generally triangular configuration providing three of saidcircumferentially spaced portions on its outer periphery.

16. A roller assembly comprising: a rigid outer roller member formed ofa first plastic material having a circular outer rim surface; end faces,and a circular inner bearing surface of longitudinally convexconfiguration,

and an inner stator member formed by a second plastic with materialinjection molded in said outer roller member

1. A method of making a roller assembly including an inner stator memberand an outer roller member rotatably and axially non-slidably supportedon the stator member comprising: molding an outer roller member of afirst plastic material in an annular shape having a circular outer rimsurface; end faces, and a circular inner bearing surface having aminimum internal diameter intermediate said end faces and a relativelylarger diameter adjacent said end faces, sealingly engaging end faces ofthe outer roller member between mold members shaped to form an enclosedmold cavity inside the annular roller member with at leastcircumferentially spaced portions of the inner bearing surface beingwall portions of the mold cavity, injecting a heat melted charge of asecond plastic into said mold cavity to fill the same, and cooling thecharge of the second plastic to a solid state before removing the moldmembers to provide a rigid stator member having at least portionS of itsouter periphery shaped in conformity with the inner bearing surface onthe roller member, said second plastic material having molding shrinkagecharacteristics to provide sufficient clearance for a running fitbetween said portions of the stator member and said inner bearingsurface on the outer roller member.
 2. A method of making a rollerassembly according to claim 1 wherein said second plastic material hashigher molding shrinkage characteristics than said first plasticmaterial.
 3. A method of making a roller assembly according to claim 1wherein said first plastic material is reinforced with glass fibers andhas a lower molding shrinkage characteristic than said second plasticmaterial.
 4. A method of making a roller assembly according to claim 1wherein said second plastic material has a melt temperaturesubstantially below the melt temperature of said first plastic materialand said second plastic material has mold shrinkage characteristicshigher than said first plastic material.
 5. A method of making a rollerassembly including an inner stator member and an outer roller memberrotatably supported on the stator member comprising, molding a rigidouter roller member of a first plastic material in an annular shapehaving a circular inner bearing surface, sealingly engaging mold memberswith the end faces of the outer roller member and with onlycircumferentially spaced portions of the inner bearing surface to form anon-circular mold cavity in the annular roller member in which otherportions of the inner bearing surface intermediate saidcircumferentially spaced portions provide wall portions of the moldcavity, injecting a heat melted charge of a second plastic material intothe mold cavity to fill the same, cooling the charge of the secondplastic material sufficient to solidify the charge before removing themold members to provide a rigid non-circular stator member havingcircumferentially spaced portions shaped in conformity with said innerbearing surface, said second plastic material having mold shrinkcharacteristics to provide a sufficient clearance for a running fitbetween said circumferentially spaced portions on the stator member andsaid inner bearing surface on the outer roller member.
 6. A method ofmaking a roller assembly according to claim 5 wherein non-circular moldcavity has a triangular configuration.
 7. A method of making a rollerassembly according to claim 5 in which said second plastic material hasmolding shrinkage characteristics higher than said first plasticmaterial.
 8. A method of making a roller assembly according to claim 5wherein said second plastic material has a higher molding shrinkagecharacteristic and a lower melting temperature than said first plasticmaterial.
 9. A method of making a roller assembly according to claim 8wherein said second plastic material has a lower coefficient of frictionthan said first plastic material.
 10. A method of making a rollerassembly according to claim 5 wherein said circular inner bearingsurface is formed with an axially varying diameter.
 11. A method ofmaking a roller assembly according to claim 5 wherein said inner bearingsurface of said outer roller member is formed with a longitudinallyvarying diameter relatively larger adjacent said end walls than at alocation intermediate said end walls and said circumferentially spacedportions on the hub member conform to said longitudinally varyingdiameter.
 12. A roller assembly comprising: a rigid outer roller memberformed of a first plastic material having a circular outer rim surface;end faces, and a circular inner bearing surface of longitudinallyvarying diameter extending between said end faces coaxial with saidouter rim surface, an inner stator member injection molded of a secondplastic material in said inner bearing surface to have at leastcircumferentially spaced portions of its outer periphery shaped toconform with the longitudinally varying diameter of the inner bearingsurface on the outer Roller member, and said second plastic materialhaving a molding shrinkage characteristic sufficiently high to provideclearance for a free running fit with said roller member when saidstator member is cool.
 13. A roller assembly according to claim 12wherein the diameter of said inner bearing surface is a maximum adjacentsaid end faces and a minimum at a location spaced inwardly from said endfaces of the outer roller member.
 14. A roller assembly comprising: arigid outer roller member formed of a first plastic material having acircular outer rim surface; end faces, and a circular inner bearingsurface of axially varying diameter extending between said end facescoaxial with said outer rim surface, and an inner stator memberinjection molded of a second plastic material in said inner bearingsurface to have circumferentially spaced portions of its outer peripheryshaped to conform with the longitudinally varying diameter of the innerbearing surface on the outer rim member and have a close running fittherewith, the peripheral portions of said stator member intermediatesaid circumferentially spaced portions being spaced radially inwardlyfrom said circumferentially spaced portions and out of runningengagement with said inner bearing surface.
 15. A roller assemblyaccording to claim 14 wherein said inner stator member has a generallytriangular configuration providing three of said circumferentiallyspaced portions on its outer periphery.
 16. A roller assemblycomprising: a rigid outer roller member formed of a first plasticmaterial having a circular outer rim surface; end faces, and a circularinner bearing surface of longitudinally convex configuration, and aninner stator member formed by a second plastic material injection moldedin said outer roller member and having at least circumferentially spacedportions of the stator member shaped by contact with the inner bearingsurface and having a shrink clearance therewith.